The invention pertains to rotatable cutting bits wherein a block on a driven body, such as a drum or wheel or blade, rotatably contains the cutting bit having a hard cutting insert which affixes to the forward end of the cutting bit. More specifically, the invention pertains to the shape of the hard cutting insert which affixes to such rotatable cutting bit.
Rotatable cutting bits are a consumable component of the overall apparatus used to break a substrate into a plurality pieces. For example, a road planing machine uses rotatable cutting bits which rotatably mount in blocks on a driven drum. An engine in the road planing apparatus drives the drum. The rotation of the drum causes the cutting bits to impinge upon a road surface, such as asphalt. The result is to break the asphalt into small pieces thereby preparing the roadway for resurfacing.
The typical rotatable cutting bit comprises an elongate steel bit body with an axially forward end and an axially rearward end. The cutting bit contains a means for retaining the bit in the bore of the block such as a split sleeve retainer. The block mounts on a rotatable drum driven by the road planing machine. A hard cutting insert, typically made from a cemented tungsten carbide (WC-Co alloy) having a cobalt content ranging from about 5 to about 13 weight percent, affixes to the forward end of the cutting bit. Typically, one brazes the hard cutting insert to the steel bit body.
The hard cutting insert is the component of the cutting bit that first impinges upon the substrate. Thus, there has been an interest in the shape of the hard cutting insert, and the influence the shape of the hard cutting insert has on the performance of the cutting bit.
Because of the importance of conserving resources, it is desirable for a hard cutting insert to minimize the volume of cemented tungsten carbide necessary to manufacture the same, and thereby conserve tungsten and cobalt, without negatively impacting on its performance characteristics.
One early cutting insert has a conical tip portion which joins to a cylindrical portion. The cylindrical portion mounts in a cylindrical bore at the axially forward end of the steel bit body. U.S. Pat. No. 3,830,546 to Kniff shows one example of such a hard cutting insert.
Another early cutting insert has coaxial and integral portions comprising a conical tip portion, a frusto-conical mediate portion which is axially rearward of the tip portion, a flange portion which is axially rearward of the mediate portion and a portion which mounts in a socket in the axially forward end of the steel bit body. One example of this style of cutting insert is found in German Offenlengungsshrift No 2846744. Another example of this basic style of cutting insert is the model C-1445-7 by Multi-Metals, a business unit of Vermont American, of Louisville, Ky., wherein there is small fillet and/or a manufacturing flat, between the cylindrical base portion and the frusto-conical inter-mediate portion. Another example of a cutting insert similar to the Multi-Metals insert, at least to the extent that there is a fillet between the frusto-conical section and the base section, is the T-104-76 cutting insert made by American Mine Tool, a division of GTE Valenite Corporation, having facilities in Bristol, Va. and Madisonville, Ky.
Another early style of cutting insert has a conical tip portion, a frusto-conical portion axially rearward of the tip portion, an arcuate portion axially rearward of the frusto-conical portion, a flange portion axially rearward of the arcuate portion, and a valve seat portion axially rearward of the flange portion. The cutting insert mounts at the valve seat portion into a corresponding socket in the forward end of the steel bit body. One example of this style of cutting insert is the Kennametal tip style 921-01135 found at one time in Kennametal C-3MLR cutting bits.
Another early style of cutting insert has a conical tip section, a frusto-conical section axially rearward of the tip section, an arcuate section axially rearward of the mediate section, and a cylindrical base section axially rearward of the mediate section. The cutting insert mounts via the base section into a socket in the forward end of the steel bit body. One example of this style of cutting insert is the T-104-13 cutting insert used in the AM722RF construction tool sold by American Mine Tool. General speaking, this cutting insert is the subject matter of U.S. Pat. No. 4,497,520 to Ojanen.
Another early cutting insert has a shape along the lines of the T-104-13 cutting insert, but further includes a small cylindrical section between the tip section and the frusto-conical section. One example of this style of cutting insert is the T-104-14 cutting insert as used in the AM722RF construction tool sold by American Mine Tool. Generally speaking, this insert is the subject matter of U.S. Pat. Nos. 4,725,099 and 4,865,392 to Penkunas et al.
Another early cutting insert has a conical tip section, a cylindrical section axially rearward of the tip portion, an arcuate section axially rearward of the cylindrical portion, a flange section axially rearward of the arcuate portion and a section by which the cutting insert mounts in a socket in the steel bit body. One example of this cutting insert is shown by U.S. Pat. No. 4,938,538 to Larsson et al. and European Patent No. 0 122 893 to Larsson et al.
Another example of an earlier cutting insert has a conical tip portion, a single arcuate mediate portion axially rearward of the tip portion, a flange portion axially rearward of the arcuate portion, and a valve seat portion axially rearward of the flange portion. The valve seat portion mounts in a socket found in the forward end of the steel bit body. Kennametal Drawing Nos. 921-01171 and 921-01173 each show this style of cutting insert which was at one time used in some Kennametal construction tools.
U.S. Pat. Nos. 4,911,503 and 4,911,504 to Stiffler et al., assigned to the assignee of the present application, show a cutting insert with a conical tip portion and a cylindrical flange portion which join together via a bell-shaped intermediate portion. Three concave surfaces, each of a different radius, blend together to form the bell-shaped surface.
Soviet Author's Certificate No 899,916 shows a hard carbide tip which mounts in a steel body. The hard insert has a conical tip section, a cylindrical mediate section integral with and axially rearward of the tip section. A large diameter cylindrical flange section is integral with and axially rearward of the mediate section. A radius joins the mediate section with the flange section. A second cylindrical section is integral with and axially rearward of the large diameter flange portion. A bore in the steel body receives the second cylindrical section so as to mount the carbide tip to the steel body.